The present invention relates to an electrostatic ink jet recording apparatus and, more particularly, to a record head for an electrostatic ink jet recording apparatus of the type depositing toner particles on a recording medium.
A non-impact recording system is attracting increasing attention because it produces only negligible noise during operation. For example, an ink jet recording scheme is capable of recording data directly on a recording medium at a high speed with a simple configuration. The method of electrostatic ink jet recording is one of several ink jet recording methods proposed in the past and uses ink consisting of a carrier liquid and toner particles dispersed therein. The electrostatic ink jet recording method selectively applies a voltage between needle-like record electrodes and an electrode positioned at the rear of a recording medium. An electrostatic force derived from the above voltage causes the toner of the ink to fly toward the recording medium.
Various methods have been proposed for the production of the record head for practicing the electrostatic ink jet recording method. For example, a metal film is formed on a ceramic, silicon or similar wafer by sputtering and then cut by dicing or similar cutting scheme in order to form grooves. This allows ink passageways and independent record electrodes to be formed at the same time and enhances accurate machining, quantity production on a wafer, and stable quantity. Japanese Patent Laid-Open Publication No. 7-276649, for example, divides a depthwise range to be cut into a zone B including an ejection port, a zone A above the zone B, and a zone C below the zone A. In the event that dicing is used to form the ejection port surface and determine the passageway length, a particular feed rate is assigned to each of the three zones A, B and C in order to improve quality and yield.
However, the conventional method of producing a record head has the following problems left unsolved.
(1) It is required in the record head that each groove be provided with a particular configuration at an end there of adjoining an ejection head and at the opposite end there as adjoining a connecting portion. It has been customary with the record head to use a groove as an ink passageway, to use a wall between nearby grooves as an ejecting portion, and to use the metal film on the top of the wall as a record electrode. Because the ejection point should be as narrow and sharp as possible, the above wall should preferably be about 15 .mu.m wide or less. The record electrode on the top of the wall must be connected to an outside electrode at the connecting portion opposite to the ejecting portion. Generally, such record electrodes arranged at a fine pitch are connected to outside circuitry by bonding or similar technology. In this sense, the 15 .mu.m wide walls or electrodes are excessively narrow.
(2) The passageways are mechanically weak for the following reason. Each passageway should preferably be as great in volume as possible, and in addition each wall (ejection point) between nearby passageways should preferably be as narrow as possible. Therefore, it is necessary for the walls to be provided with a high aspect ratio. However, when the grooves each having a preselected width and a preselected depth are formed, they are mechanically extremely weak and reduce the yield of quantity production.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-309993, 7-276649 and WO 93/11866.